1. The Field of the Invention
The present invention relates to methods and compositions for controlling the rheology of emulsion compounds and explosives containing an emulsion. More particularly, the present invention is related to an emulsion with a polymerizing and/or crosslinking agent which permits the preselection of a desired rheology of the subject emulsion compound.
2. Background of the Invention
Explosive compositions are frequently used in construction and mining related enterprises. The physical characteristics of explosive compounds vary with the intended use. In some circumstances it is desirable to utilize an explosive composition whose viscosity is so low that the explosive composition may be pumped into its intended site. On the other hand, it may be desirable to utilize an explosive composition which alone is rigid enough to withstand the weight of stacking in storage or as packaged material, when stacked vertically in a borehole.
In the last few decades, developments in mining explosive technology have produced explosives far different from nitroglycerine-based explosives used in the past. Explosives are now made from components which are much less expensive and are less dangerous to prepare, transport and use. These developments have resulted in slurries and explosives containing an emulsion.
The development of slurries has resulted in the use of thickening agents such as water-soluble gums, especially guar gum, allowing control of the rheology of continuous phase of the slurry and, hence, the slurry matrix. Slurries continue, however, to be plagued with crystallization of the discontinuous phase. Slurries are prone to crystallization at low temperatures. This compromises the intimacy of the mixing of the oxidizers and fuels and results in a loss of sensitivity. This problem is particularly acute in small diameter applications. Loss of sensitivity is overcome by employing expensive ingredients such as paint grade aluminum, TNT, monoethanolamine nitrate, hexamethylenetetramine nitrate, ethylene glycol mononitrate, and the like. What is needed is an explosive composition whose sensitivity is not compromised by crystallization, but which retains the versatility of rheology control exhibited by slurries or water-gel explosives.
Explosives containing an emulsion are now well-known and overcome many of the problems encountered with previous explosive formulations. The discovery of water-in-oil emulsions has resulted in pumpable fluid-like explosives containing an emulsion which prove superior to slurries for many uses. Generally, emulsions include two separate phases. These phases comprise a discontinuous internal phase of an aqueous solution of oxidizers and a continuous external phase of a carbonaceous fuel, such as oils and waxes, and an emulsifier. The typical explosive containing an emulsion also contains sensitizers in order to render them detonable. One of the favorable features of explosives containing an emulsion is the fact that the surface area of contact between the fuel phase and the oxidizing phase is increased such that the fuel phase and the oxidizing phase are more intimately interspersed and, hence, more sensitive and faster reacting upon detonation.
Emulsions have provided some solutions to problems of water resistance, separation of components, and loss of detonability at low temperatures. Explosives containing water-in-oil emulsions also have other advantages. They are safer because they are less sensitive to mechanical shock, and less expensive because the principal component ingredients of water, oil, ammonium nitrate, emulsifying agents, and sensitizers are available at relatively lower cost.
When emulsions are properly prepared, the interspersed oxidizer droplets of the oxidizing phase are so small that they are able to be supercooled. As a result, a highly concentrated aqueous solution with a crystallization temperature well above room temperature can be obtained and incorporated into the discontinuous oxidizing phase. Such an aqueous solution will not experience crystallization even upon cooling to a temperature well below the crystallization temperature. This preserves the intimacy of the mixing and the desired sensitivity. However, currently available emulsions have limited shelf life because of the tendency of the aqueous phase to crystallize and for such crystals, by rupturing the barriers between droplets, to grow. The emulsion then loses sensitivity.
The rheology of currently available explosives containing an emulsion is dependent largely upon the physical consistency of the continuous fuel phase and on the volume ratio of oxidizer to fuel phases. Rheology control manipulates the phase volume ratio of the oxidizer solution of the discontinuous phase to the continuous fuel phase, and/or selectively varies the size of the droplets of the oxidizer solution, and/or selectively varies the viscosity of the continuous fuel phase. The choice of phase volume ratio dictates the rheology of the emulsions and explosives containing an emulsion. For example, if the ratio of oxidizer solution to fuel is large the resulting emulsions are stiff. Similarly, if the solution droplets are small the resulting emulsions are stiff. Furthermore, if the fuel phase comprises a thick oil the resulting emulsions are highly viscous, or if the fuel phase comprises a wax the resulting emulsions have a high degree of plasticity.
The ability to control the rheology of the emulsion or explosive containing an emulsion becomes very apparent when considering the manufacturing of explosives containing an emulsion. As stated, oils and waxes are selectively chosen to obtain the desired rheology of an emulsion or explosive containing an emulsion. If, for example, it is desirable to cartridge the explosive containing an emulsion, or to assure that air bubbles or other discontinuous phases are held in place, the oils or waxes must be fluid at the temperature of manufacture in order to form and refine, and then pour or pump the emulsion. As a result, the rheology of the final composition is then dependent on temperature. Even emulsions and explosives containing an emulsion containing waxes which are relatively stiff at the lower temperatures of use are relatively and often undesirably soft at higher temperatures of use. Change in the rheology with temperature is contrary to the constant environment needed to effectively disperse or maintain in dispersion a discontinuous oxidizing phase or sensitizing agent. In other words, temperature changes work not only a change in the rigidity of the composition itself, but also detrimentally influence the ability of the emulsion or explosive containing an emulsion to hold or lock the discontinuous oxidizing phase and/or sensitizers in place.
An explosive containing an emulsion whose composition permitted the user to select the rheology of the ultimate explosive containing an emulsion, much as is possible with water-gel explosives, would be much more desirable. Such a composition would provide an explosive containing an emulsion which is capable of effectively stabilizing the continuous and discontinuous phases over a wide range of temperatures such that the explosive containing an emulsion would be less sensitive to temperature changes. Similarly, it would be an advancement in the art if the rheology of a given emulsion or explosive containing an emulsion would permit the control of other significant characteristics of the composition, such as waterproofing, surface adhesion, and wetness. Indeed, what is needed is a polymerizing agent or crosslinker which permits the user to select the desired rheology.
Therefore, it would be a further advantage and improvement in the art if the rheology of an emulsion or explosive containing an emulsion could be controlled to produce an emulsion or explosive containing an emulsion which is more stable, i.e., less prone to crystallization of the oxidizer salts in the solution of the discontinuous phase and to subsequent growth of the crystals.
Such an emulsion and explosive containing an emulsion are disclosed and claimed below.